The present invention relates to signals detection used in receivers and, more particularly, to methods and corresponding devices for joint signal detection and direction of arrival estimation, based on the ability to identify both the existence and direction of arrival of a required signal featuring known characteristics, before it is forwarded to a modem. Optionally, after identifying the existence and the direction of arrival of a required signal, the direction of arrival is entered into a beamformer to obtain the signal coming from the required direction of arrival. The calculated signal is then entered into a modem.
Basic principles and details relating to joint signal detection and direction of arrival estimation needed for properly understanding the present invention are provided herein. Complete theoretical descriptions, details, explanations, examples, and applications of these and related subjects and implementations are readily available in standard references from the fields of telecommunication, signals detection and, spatial scanning.
Prior art includes various teachings of signal characteristics detection. In U.S. Pat. No. 6,347,234, issued to Scherzer, there is disclosed a method of enhancing signal quality (carrier to interference) in both up and downlink of wireless point to multi-point CDMA service implements basic radio direction finding techniques to allow for optimal diversity combining in an antenna array employing large number of elements. This prior art is implemented through the use of very small bit counts arithmetic and capitalizing on finite alphabet signal structure or a known training sequence. Alternate implementations can use floating point data representations. The method facilitates ASIC implementation, thereby enabling distributed processing to achieve the required computation practicality. The method utilizes the uplink channel data to determine the downlink spatial structure (array beams) to enhance downlink carrier to interference and hence, increase downlink capacity.
However, Scherzer is notably limited because it describes a specific CDMA implementation that can not be used for other types of signals. Additionally, the disclosed method is particularly described with respect to channel estimation featuring channel estimators, and is not obviously extendable to estimating the characteristics of the received signals.
In U.S. Pat. No. 6,489,923, issued to Bevan et al. there is disclosed a mechanical system for position location for a mobile telecommunications system by estimating its bearing and range from a cell site. A multi-element direction finding antenna at the cell site receives signals from the mobile station and a receiver circuit estimates the bearing using the relative phase of signals received at different antenna elements and estimates the range by measuring round trip delay of signals to and from the mobile station. Motion of the mobile station can introduce errors into the bearing estimate due to frequency offset and frequency spread when element sampling is non-simultaneous. Compensation for these errors is introduced by using signal samples successively received at the same antenna element to estimate Doppler frequency offset and spread. It is necessary to ensure accurate calibration of the direction finding antenna and the receiver circuit. This is done by injecting calibration signals into the circuit near the antenna or into the antenna itself from a near field probe. Other aspects of calibration, such as antenna position, are calibrated using a remote beacon. A beacon emulating a mobile station but at a fixed, known location, or a beacon at an adjacent cell site may be used.
However, Benav et al. disclose a mechanical system and cells fragmentation. There is no description or suggestion for antenna array with no moving parts. Moreover, Bevan et al. provide no description or suggestion relating to joint signal detection and direction of arrival estimation.
Other prior art solutions are analog solutions in RF. Implementation of analog systems requires putting a modem on each beam. However, this solution is highly expensive, which is why current analog solutions do not provide the novel functionality of the present invention.
To date, the inventor is unaware of prior art teaching of a digital solution for joint signal detection and direction of arrival estimation, before the signal is forwarded to a modem.
There is thus a need for, and it would be highly advantageous and useful to have a method and corresponding device for joint signal detection and direction of arrival estimation, based on the ability to identify both the existence and direction of arrival of a required signal featuring known characteristics, before it is forwarded to a modem. Moreover, there is a need for such a method, which is significantly simpler, more rapid, and therefore, more cost effective, than currently used techniques for signal detection and direction of arrival estimation.
To one of ordinary skill in the art, there is thus a need for identifying required signals using inexpensive hardware. As a result, there is a need to identify required signals without using a huge number of calculations. Using a correlator in the time domain to identify required signals requires a huge number of calculations, and therefore is expensive.
Furthermore, most communication standards contain a transmission power limit. Increasing the gain of a transmitting antenna decreases the transmission power. Therefore, there is thus a need for, and it would be highly advantageous to have a method and corresponding device that increase transmission and reception ranges without increasing the antenna's gain.
One of the possible solutions for increasing the transmission and reception ranges without increasing the antenna's gain is to use the spatial scanning method, as known in the radar art. However, the spatial scanning method is notably limited because it is time-consuming.
It is also desirable to have a method and device for sniffing the medium in order to filter out interfering signals. In an exemplary embodiment of the present invention, an IEEE 802.11 type of wireless network is implemented. In this exemplary embodiment, interfering signals that should be filtered out are, for example, Bluetooth signals, Cordless phones signals, etc.